1. Field of the Invention
The present invention relates to a swing control system and method for a construction machine using an electric motor. More particularly, the present invention relates to a swing control system and method for a construction machine using an electric motor, which can provide the output characteristic that is similar to that of the existing hydraulic system in place of a hydraulic motor used to rotate an upper swing structure of a construction machine, and particularly a hydraulic excavator.
2. Description of the Prior Art
In the related art, an upper swing structure of a construction machine, and particularly a hydraulic excavator, including the upper swing structure is rotated by a hydraulic motor. The hydraulic motor has a high torque output and the characteristic of a hydraulic system of which the control is relatively simple. Since it is difficult that any other actuator replaces the hydraulic system having the high torque output, the hydraulic system has mainly been used in heavy equipment and so on. The hydraulic drive system using a hydraulic motor has low energy efficiency due to resistance in a control valve that controls the discharge rate of a hydraulic pump, a pressure loss in pipes, generation of a surplus flow rate in a hydraulic circuit, and the like. Also, when the upper swing structure stops after a swing operation, braking energy is consumed as heat energy, and this causes the efficiency of the hydraulic motor to be lowered.
Accordingly, the use of an electric motor as an actuator has been known to heighten the energy efficiency. The efficiency of an electric system is far superior to that of the hydraulic system. In the case of using the electric motor as the swing motor of the construction machine, the energy efficiency is improved, but the response of the electric motor to lever manipulation is too sensitive in comparison to that of the hydraulic drive system, and this causes the manipulability of the electric motor to become deteriorated rather than that of the hydraulic drive system.
In order to solve this problem, Korean Patent Application Publication No. 2005-0000530 discloses the related art that adopts an electric swing motor in place of a hydraulic motor.
According to the technique in the related art, complicated governing equations are derived from an emulation model of an excavator hydraulic system, and the hydraulic system is controlled through real-time operation. Accordingly, a lot of control operation time is required due to the complicated calculation, and a high-performance processor that can perform high-speed operation is required.
Recently, with the development of technology, a permanent magnet synchronous motor (PMSM), which can generate a high-torque output and has a superior control performance, has been developed. This PMSM can replace the current hydraulic system to solve the problems of the hydraulic system, and the braking energy occurring when the swing system stops can be withdrawn through the driving of electric generation of the PMSM to improve the efficiency. As the swing system is changed from the hydraulic motor to the PMSM, the efficiency is heightened. However, if the characteristic change due to the change of the actuator occurs, existing users may feel inconvenience, and this may cause the working efficiency to deteriorate and cause a user to avoid purchase of a hybrid excavator.